The present invention relates generally to methods for hot forming metals and alloys, and more particularly to a method for controlling the forging process for coarse grain materials to simultaneously enhance forgeability and refine microstructure.
Hot working behavior of many high melting temperature alloys is sensitive to starting microstructure and deformation rate. In as-cast ingot metallurgy metallic and intermetallic alloys, particularly single phase alloys, coarse grain microstructures are common. Coarse structures are also common in materials previously heat treated or worked at temperatures near (&gt;90% of) the melting point. When such coarse grain structures are hot worked, as in isothermal or conventional forging, fracture may result if the deformation rate is too high, particularly if secondary tensile stresses result such as from geometric, friction or other causes. The materials are therefore usually forged at relatively low true effective strain rates (.about.0.001 in/in/sec) in hydraulic presses. At these rates, dynamic restorative processes such as recovery and recrystallization occur at sufficient rates to prevent generation or growth of microscopic defects such as intergranular cracks. In many high melting temperature alloys such as those based on nickel or titanium and intermetallic materials such as the aluminides, silicides and beryllides, dynamic recrystallization predominates during hot working and usually results in refinement of grain size relative to that of the starting materials. The degree of refinement increases as deformation rate is increased and/or temperature of deformation is decreased.
The invention provides a method of controlling deformation rate during hot forging to recrystallize coarse grain structures several times during deformation while simultaneously avoiding fracture. The method comprises initial minimum deformation at a suitably low rate in order to effect an initial increment of dynamic recrystallization and grain refinement without fracture, and then further deformation(s) at increased rate(s) to re-recrystallize and further refine the grain structure.
The invention may be used for hot forging a wide range of ingot metallurgy alloys used in aircraft structures, engines, automotive components and the like. Forging response in coarse grain materials having narrow working regimes can be enhanced to improve product yield while reducing overall forging time and final product cost. The process may be used for both primary fabrication and finish forging of components, particularly in production operations based on isothermal forging.
It is therefore a principal object of the invention to provide an improved hot forging method.
It is a further object of the invention to provide a method for hot forging coarse grain alloys.
It is yet another object of the invention to provide a method for controlling the forging process for coarse grain materials to simultaneously enhance forgeability and refine microstructure.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.